The present invention relates to a laminate, a method for producing the same, and a thermoplastic foam adhesive. In particular, the present invention relates to a laminate comprising a pair of thermoplastic resin members having fluctuations in the clearance between their adhesion surfaces, which are adhered with a good adhesion strength, a method for producing such a laminate, and a thermoplastic foam adhesive which is used in the production of such a laminate.
As interior members of vehicles such as automobiles, laminated members comprising a skin material made of a vinyl chloride resin, which is laminated on a substrate using a polyurethane foam. The substrate is usually formed from an ABS resin, a modified polyphenylene ether resin, or polypropylene (cf. JP-B-5-1123, JP-A-8-48201, etc.) The polyurethane foam layer imparts cushioning feeling to the laminated members, absorbs the unevenness of the back surface of the skin material, and strongly adheres the skin material and the substrate. As described in JP-A-6-106682 and JP-A-7-214672, a laminate having an adhesive comprising a terpene resin, which is interposed between the skin material and the substrate to increase the adhesion strength between them, is also known.
Meanwhile, as part of the measures to protect the environment, it is required to increase a recycling rate of materials which construct automobiles, and it is the obligation to use parts at least 90% of which based on the weight of the automobiles can be recycled.
However, in the case of the conventional laminate members comprising the skin material of the vinyl chloride resin, the polyurethane foam and the ABS resin substrate, it is very difficult to separate the once laminated materials and recycle them, since the members comprise the different materials and, in addition, use the thermoplastic resin and the thermosetting resin at the same time, and they are firmly adhered. Thus, it may be contemplated that, when resinous materials which are used to produce interior and exterior members are unified in the same resin, the materials can be easily recycled and thus the recylcing rate can be increased.
JP-A-10-244885 discloses an interior member for a vehicle comprising a skin material, an intermediate foam layer and a core, all of which are made of polyolefin resins and a method for the production of such a member. However, the skin material, intermediate foam layer and core are all molded by a powder slush molding method, the foam layer cannot absorb the fluctuation of the clearance between the skin material and the core (substrate) due to the unevenness formed on the adhesion surfaces.
JP-A-60-248749 discloses a foam adhesive comprising a styrene-butadiene copolymer as a primary component. JP-A-2-199164 discloses a resin composition comprising a terpene-phenol resin to increase the adhesion between the resin composition for a skin material and a polyurethane foam. However, in this case, the resin composition may have decreased quality such as stickiness.
One object of the present invention is to provide a thermoplastic resin laminate, all the layers of which are formed from thermoplastic resins, which can absorb the fluctuation of the clearance between the layer members, and the layer members of which are strongly adhered.
Another object of the present invention is to provide a resinous laminate, substantially 100% of which can be recycled.
A further object of the present invention is to provide a method for producing such a thermoplastic resin laminate.
A yet further object of the present invention is to provide a thermoplastic foam adhesive which can be used to produce such a laminate.
According to the first aspect of the present invention, there is provided a laminate comprising
a pair of thermoplastic resin members having fluctuation of clearance between the adhesion surfaces thereof, and
a thermoplastic material foam layer which adheres said pair of the thermoplastic resin members.
According to the second aspect of the present invention, there is provided a method for producing a laminate comprising the steps of:
supplying an adhesive thermoplastic material containing a foaming agent in a space between adhesion surfaces of a pair of thermoplastic resin members having fluctuation of clearance between the adhesion surfaces,
foaming said adhesive thermoplastic material, and
adhering said pair of thermoplastic resin members with said adhesive thermoplastic material.
According to this production method, the laminate of the present invention, which has a substantially constant thickness, is recycled and has good cushioning properties, can be easily produced.
According to the third aspect of the present invention, there is provided a thermoplastic foam adhesive comprising a styrene-butadiene rubber, 3 to 10 wt. parts of microcapsules which contains a foaming agent and comprises a shell of a vinylidene chloride-acrylonitrile copolymer per 100 wt. parts of the adhesive, and a mixed solvent of toluene and cyclohexane, and having a solid content of 30 to 60 wt. %.
This thermoplastic adhesive is preferably used as the material of the thermoplastic material foam layer of the laminate of the present invention, or as an adhesive thermoplastic material used in the method for producing a laminate according to the present invention.
Herein, the xe2x80x9cfluctuation of clearancexe2x80x9d is intended to mean the fluctuation of the clearance between the adhesion surfaces of a pair of thermoplastic resin members caused by the unevenness on the adhesion surfaces. In the concrete, the present invention deals with the fluctuation of clearance generated by the surface roughness of the adhesion surface with the maximum height Rt of at least 7.0 xcexcm, wherein the maximum height Rt of the surface roughness is determined by a distance between two lines which are drawn in parallel with the center line of the roughness curve in the region of the roughness curve cut out along the standard length to sandwich the region.
The laminate of the present invention has the characteristics such that its thickness is substantially constant, it can be recycled, and it has a high adhesion strength and also good cushioning properties. When the laminate has a thermoplastic resin foam layer, the cushioning properties are further improved, or the freedom of the selection of the material for the thermoplastic material foam layer increases, since the cushioning properties are attained by the thermoplastic resin foam layer.
In one preferred embodiment of the laminate according to the present invention, the thermoplastic resin foam layer is provided on the adhesion surface of the thermoplastic resin member on the skin side, and at least one of a terpene resin and a low molecular weight modified polyolefin is added only to the thermoplastic resin foam layer among the thermoplastic resin member and the thermoplastic resin foam layer. In this case, the adhesion strength can be increased without the deterioration of the quality such as the tackiness of the skin material, etc.
In another preferred embodiment of the laminate according to the present invention, the thermoplastic resin member on the skin side and the thermoplastic resin foam layer are molded by a powder slush molding method, and the amount of the terpene resin and/or the low molecular weight modified polyolefin to be added is from3 to 20 wt. parts based on 100 wt. parts of the thermoplastic resin in the thermoplastic resin foam layer. In this case, the adhesion strength can be increased without the deterioration of the quality such as the tackiness of the skin material, etc.
In one preferred embodiment of the method of the present invention, at least one of the thermoplastic resin members is molded by a powder slush molding method. When the thermoplastic resin member is produced by powder slush molding, its thickness greatly fluctuated, and in turn its adhesion surface has large unevenness. Even in such a case, the method of the present invention has no disadvantage, since an adhesive thermoplastic material containing a foaming agent is used.
In another preferred embodiment of the method of the present invention, a layer of a thermoplastic resin containing a foaming agent is formed on the adhesion surface of at least one of the thermoplastic resin members, and foamed in the course of adhering the layer of the thermoplastic resin to the thermoplastic resin member. In this case, the cushioning properties of the laminate are further improved, or the freedom of the selection of the material for the adhesive thermoplastic material increases.
In a further preferred embodiment of the method of the present invention, at least one of the thermoplastic resin members is molded by powder slush molding and then the layer of the thermoplastic resin containing the foaming agent is also formed by powder slush molding. In this case, the laminate can be easily produced, and the fluctuation of the foaming of the thermoplastic resin containing the foaming agent is suppressed since a temperature distribution in the cavity of the mold can be narrowed because of the presence of the already molded thermoplastic resin member.
In a yet another preferred embodiment of the method of the present invention, a thermoplastic resin containing a foaming agent is applied on the adhesion surface of at least one of the thermoplastic resin members, and foamed in the course of adhering the layer of the thermoplastic resin to the thermoplastic resin member. In this case, the cushioning properties of the laminate are improved, or the freedom of the selection of the material for the adhesive thermoplastic material is increased.
In a further embodiment of the method of the present invention, a laminate is produced by the following steps:
1) providing a molding mold having the first and second molds,
2) setting one thermoplastic resin member, which has been molded by powder slush molding, in the first mold,
3) applying an adhesive thermoplastic material containing a foaming agent to the other thermoplastic resin member and setting the other thermoplastic resin member in the second mold, and
4) heating the adhesive thermoplastic material containing the foaming agent to foam the foaming agent, and closing the first and second molds so that a pair of the thermoplastic resin members are adhered with the adhesive thermoplastic material in the mold.
In this case, the heating is surely and easily carried out to foam the foaming agent, and the accuracy of the molding is increased.
In a further preferred embodiment of the method of the present invention, in the above step to set the thermoplastic member in the first mold, a layer of a thermoplastic resin containing a foaming agent is formed on the adhesion surface of at least one of the thermoplastic resin members which is molded by powder slush molding and heated to foam the foaming agent so that the layer and the thermoplastic resin member are adhered, and then the thermoplastic resin member carrying the foamed layer of the thermoplastic resin is set in the first mold. In this case, the cushioning properties of the laminate are improved, or the freedom of the selection of the material for the adhesive thermoplastic material is increased.
In a yet further preferred embodiment of the method of the present invention, at least one of a terpene resin and a low molecular weight modified polyolefin is added only to the thermoplastic resin containing the foaming agent. In this case, the adhesion strength can be increased without the deterioration of the quality such as the tackiness of the skin material, etc.
In a yet further preferred embodiment of the method of the present invention, when the first and second molds are being closed, the adhesion surface of the thermoplastic resin member carrying the adhesive thermoplastic material, which is set in the second mold, is heated. In this case, the impregnation of the adhesive is accelerated, and thus the adhesion strength is increased.